The long-term goal is to understand the effect of flow and fluid mechanical stresses on the arachidonic acid metabolism of leukocytes, platelets and endothelial cells. Initial studies from our laboratory have indicated some quite dramatic stress-metabolism coupling in each of these cell types. Proposed work will center on understanding the mechanism of membrane signal transduction for this unique (and physiologically important) stimulus. Possibilities include direct alteration of internal calcium levels via recently described stretch-activated calcium channels. Alternatively, membrane stresses may cause local changes in fluidity, leading to phospholipase C activation of the phosphoinositol cycle (similar to receptor binding), with subsequent activation of cell metabolism. We will examine the latter hypothesis by use of inhibitors of different steps in PI cycle signaling. In addition, the exchange of metabolites between cells under controlled flow conditions will be examined using radiolabeled arachidonic acid combined with HPLC or radioimmunoassay and TLC. We hypothesize that both the level of stress and the rate of change of stress acting on the cell membrane are important factors in modulating the effect of flow on metabolism. Experiments will vary in exposure time, the stress magnitude and the time history of stress application. Specially designed viscometers and flow chambers will be employed. The endothelial cell cultures will be directly visualized utilizing video microscopy coupled with digital image processing. The results should be of importance in understanding the role of flow in ischemic events and reperfusion. Many of the metabolites produced are extremely bioactive and can lead to changes in vessel permeability, cell adhesion and smooth muscle tone - all of which may be important in the outcome of stroke.